This research will compare 4 tests purported to differentiate cystic fibrosis (CF), homozygotes, heterozygotes and normal homozygotes. We will test a minimum of 100 individuals, with approximately equal numbers of CF patients, obligate heterozygotes, other family members at risk to be carriers, and contrast controls. All material will be coded and tested blindly. We will measure total protease activity of activated plasma and cultured fibroblasts, the dexamethasone sensitivity of fibroblasts, and the presence of the serum CF factors as identified by isoelectric focusing. We will analyze the data for reliability of each test, singly, or in sequence. We hope to make recommendations for future carrier detection studies and pre-natal diagnosis. We will also look for genetic heterogeneity, if it exists and is detectable with this protocol.